Farmville developer Zynga filed a lawsuit against third-party, real-money-trading marketplace PlayerAuctions.com over the unauthorized sale of virtual currency/goods for Zynga games and the use of its copyrighted images.

In Zynga's free-to-play titles on Facebook, players earn in-game cash and digital goods through playing games, participating in offer-based ads, or spending real money through first-party options. The company's Terms of Service restricts players from selling virtual currencies or goods for real money to each other, and prohibits third-party services from selling them, too.

Zynga's lawsuit, which was filed with the California Central District Court last week, accuses PlayerAuctions.com of advertising and selling virtual currency/items for titles like Farmville, Mafia Wars, and Texas HoldEm Poker, and alleges that the service transfers those purchased goods within the games themselves using player-to-player trading features.

Furthermore, Zynga says the site sells those digital items and cash at "prices that are substantially lower than the prices paid by users who obtain their 'virtual currency' or 'virtual goods' from Zynga". With Texas HoldEm Poker, for example, players can buy 75,000 chips from Zynga for $5 or 1 million chips from PlayerAuctions.com for $5.45.

Playerauctions.com sells in-game currency, power-leveling services, game guides, items/equipment, and even accounts for a number of popular MMOs, including World of Warcraft, Aion Online, EverQuest, Final Fantasy XI, and others -- all of which forbid the unauthorized third-party sale of these virtual goods and services.

The Farmville developer also says the site is using its trademarks and copyrighted images without permission to advertise the sale of the virtual currencies and goods, according to a report from the Los Angeles Intellectual Property Trademark Attorney Blog. The studio has asked for injunctive relief and is suing for damages in an amount Zynga hopes to prove at trial.